The long-range goal of the proposed research is to define the rapid signaling mechanism(s) by which estrogen (E2) acts in hypothalamic POMC (beta-endorphin) and dopamine neurons to modulate homeostatic functions such as reproduction, temperature regulation, stress responses, feeding, motivation and reward; and to incorporate this information into a cellular model of membrane-initiated signaling by E2. Understanding these novel, fast actions of E2 and how they relate to its genomic actions will provide insight into a fundamental problem facing approximately 50 million women in need of hormone replacement therapy. E2 is neuroprotective, prevents hot flushes, has a positive influence on mood and affect, is protective against osteoporosis but increases the risk of breast and uterine cancers. Selective estrogen receptor modulators (SERMs) that produce the beneficial effects of E2 in the central nervous system (CNS) but lack the cancer risk profile of E2 are greatly needed. It has been suggested that the nuclear estrogen receptors ER alpha and ER beta are responsible for all of the actions of E2, but our studies provide strong evidence for a novel membrane-associated E2 receptor that mediates rapid signaling in the CNS. The receptor has not yet been identified nor is the nature of its coupling to effector systems completely understood. We recently synthesized the first SERM, STX, that specifically targets the membrane receptor, which will allow us to rigorously characterize and eventually identify the membrane ER. Our hypothesis is that the rapid effects of E2 are due to its binding to a G protein-coupled receptor that activates kinase pathways to attenuate GABA-B and mu-opioid receptor activity. In this proposal, we seek to elucidate the cellular cascades activated by STX and to further characterize the receptor mediating these effects. We will use a unique range of cellular, molecular and chemical tools to characterize the Gq-coupled E2 receptor, its coupling to signaling pathways in hypothalamic neurons and its functional consequences. The specific aims are: (1) To test whether STX uses the same receptor-mediated signaling pathway as E2 to uncouple GABA-B and mu-opioid receptors from K+ channels in POMC and dopamine neurons. (2) To test whether STX alters gene expression in a sub-group of E2-regulated transcripts that are critical for synaptic transmission in hypothalamic neurons. (3) To test whether the rapid effects of E2 and S TX on POMC and dopamine neurons are present in ER alpha and beta-deficient mice, and based on the results develop a cloning strategy for the membrane ER. These studies will not only identify the pathway(s) that is critical for rapid signaling in hypothalamic neurons but also should allow the development of new SERMs specifically targeting critical brain circuits involved in the control of homeostasis in the female.